1. Technical Field
The present invention relates generally to methods and apparatuses for polishing semiconductor devices and, more specifically, methods and apparatuses used in the chemical mechanical polishing of semiconductor and related devices. Still more specifically, the present invention relates to methods and apparatuses for cleaning a conditioning device used for the conditioning of polish pads used in a chemical mechanical polishing system.
2. Description of the Related Art.
As the size of electronic devices and circuit dimensions become smaller, it becomes increasingly desirable to planarize and smooth wafer surfaces. Specifically, with smaller circuit dimensions, the value of each unit area of a semiconductor wafer becomes higher because an increasing percentage of the wafer surface is used for surface components. In order to reliably form an integrated circuit with advanced circuit designs that use higher percentages of the wafer surface area for these smaller surface components, it is desirable that the wafer surface area be relatively defect free or that the defects be reduced below levels which were previously acceptable.
Currently, to meet the demand for semiconductor wafers with a highly planarized and smooth surface, manufacturers rely upon chemical mechanical polishing (CMP) processes. CMP can be used for planarizing bare silicon wafers, inter-level dielectrics, metals, and other materials. CMP involves the use of a polish pad in combination with a chemical mixture known as a slurry. The slurry may or may not contain an abrasive component. CMP has proven useful for fabrication of integrated circuits, miniature optical and mechanical devices, disk drives, magnetic heads, and may other devices.
Typically in a CMP process, the wafer being processed is held on a carrier which may be rotated while the face of the wafer is pressed against a resilient polishing pad that is attached to a rotating platen or a traveling belt arrangement. A slurry is applied to the pad to lubricate the interface between the wafer and the polishing pad. The slurry also serves the function of mildly abrading or affecting the surface of the wafer due to its abrasive and/or other components. Chemicals may be added to the slurry that catalyze reactions which break chemical bonds within the polished material to help increase the polishing rate. An abrasive component may or may not need to be present.
Polishing pads are typically formed from a polymer with a cellular microstructure with numerous voids between individual cells that serve as pockets that hold slurry. As the pad contacts the wafers, the cellular microstructure tends to abrade or wear, which changes its ability to trap slurry. The result is changes in the polishing processes such as polish rate change, uniformity change etc. In order to combat these effects, a pad conditioning system can be employed.
A pad conditioning system typically presses an abrasive conditioning disk or ring onto the pad surface and has the ability to move the conditioning disk to various locations or tracks on the pad surface. These conditioning systems are only partially effective because as they condition the pad, they cause the pad to wear out faster thus, decreasing the usable life of the pad. Conditioning systems also tend to elevate defect levels because they shed particles themselves and tend to break particles free from the pad surface. Conditioning disks and rings also tend to become covered with polishing slurry which if not carefully cleaned away, can agglomerate as time goes by and shed particles onto the polish pad, thereby causing defects on the wafers being polished.
Recently, systems have been developed which employ ultrasonic energy in combination with pad conditioning during the conditioning process in an attempt to remove particles from the polish pad and to effect the pad conditioning process itself. Examples of this technique are found in related U.S. Pat. Nos. 5,868,608 and 6,168,502 as well as U.S. Pat. No. 5,906,754. These patents address the issue of applying ultrasonic energy for polish pad conditioning but do not address the issue of cleaning the conditioning device itself, outside of the conditioning process. Particles coming from contaminants on and within the conditioning disk continue to be problematic for CMP processes.
Therefore, there is a need for an improved method of cleaning the pad conditioning device in order to remove the source of these particles.